Radio shielding means



Jw ne 27; 1939. M. F. PETERS 2,163,624

RADIO SHIELDING MEANS Filed May 11, 1938 2 Sheets-Sheet l INVENTORMELV/LLE F. PETERS BY W mam- ATTORNEY June 27, 1939. M PETERS 2,163,624

RADIO SHIELDING MEANS Filed May 11, 1938 2 Sheets-Sheet 2 INVENTORMELV/LLE F. PETERS ATTORNEY Patented June 27, 1939 I UNITED STATESPATENT OFFICE 7 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3'10G. 757) This invention relates to means for shielding the ignitionsystem of an internal combustion engine to prevent interference with theoperation of radio receiving sets due to energy-radlated from suchignition system, and more particularly to apparatus adapted to be usedon an aircraft in conjunction with the metal cowiing for the engine andthe metal of the nacelle.

Among the several objects of this invention are:

To provide simple and effective means for preventing radiation from theignition system of an internal combustion engine; I

, To provide means for shielding an ignition system wherein the metal ofsurrounding parts of the structure in which the ignition system isinstalled assists in the shielding function;

To provide radio shielding means that will introduce no difilculties dueto retention of heat by the shielding means;

To utilize readily formed shapes of foraminous electrically conductingmaterial around certain of the partsto be shielded.

Further objects of this invention will become apparent from thedescription that follows.

In the drawings: Fig. 1 discloses one embodiment of my inven tionwherein the magneto and certain other elements are enclosed in aforaminous electrically conducting shield and the ignition leads aregrounded thereon;

Fig. 2 shows a variation of my novel shielding means whereinsubstantially flat members in the form of shielding walls are disposedon opposite sides of the magneto and certain other parts and aregrounded on the engine cowiing;

Fig. 3 shows novel means'for suppressing very short waves.

In Fig. 1 there is depicted, by way of illustration, an aircraft engine3 mounted in a metal nacelle l and having disposed around it metalcowiing 5. Ignition current is suppliedto the cylinders 6 by way ofignition leads I from 'a magneto 8. grounded to the engine 3 and aforaminous metallic enclosure l0 substantially in the form of a cylinderclosed at one end is disposed around the magnetos 8 with the open endthereof closed by and grounded to the ring 9. That portion of eachignition lead I that lies outside the member III is enclosed in aconductive shielding element ii that is grounded at one end to theengine adjacent the respective spark plug and at the other end to thering 9 or to the member ID, as is most convenient in view of theposition of the lead. While the return current could pass through theengine back to the magneto the well known proximity effect results inits following the path through the shielding elements II. It is obviousthat all radiation from the magnetos A ring 9 "is disposed around and.

. of several frequencies.

and associated devices from those parts of the leads I within the memberI 0 will be eflectively intercepted by the member III. the ring 9 andthe portion of the engine structure within the member ID. It is knownthat if the return current passes through the engine there is resultantradiation and interference with radio equipment adjacent thereto.

The embodiment of my invention shown in Fig. 2 differs from that in Fig.1 in that, the

foraminous conducting member 15 extends completely across the spacewithin cowiing 5 in the form of a wall, rearwardly of the magneto 8. Asecond wall .or foraminous shielding member It, extends from the cowiingto engine 3 forwardly of magneto 8, it being understood that both ofmembers l5 and l2 are electrically grounded to the cowiing 5 and thatmember I2 is also grounded to engine 3. Here, as in Fig. 1, the ignitionlead I is shielded exteriorly of the space between members i5 and I! bywell-known flexible shielding elements II that are grounded at one endto the engine and at the other end to the foraminous members.

' It has been found that adequate shielding is had when the mesh ofmembers such as I2 is sufficiently large that there is no appreciableincrease in air resistance due thereto. There are numerous advantagesinherent in mypresent invention not found in the types of shieldingheretofore known wherein the ignition wires are carried in a rigidshielding manifold. Among such advantages are ease of removing andreplacing ignition leads, the absence of outlets that may result inbends in the leads, ready access of air to the shielded parts to carryoff heat conaround the ignition system in such position that radiationtherefrom is prevented from passing out into space by repeatedreflection from such metallic parts. That is; the auxiliary apparatussuch as carburetors, pumps, oil lines, etc., all aid in the shieldingand if theleads are' shielded from the magneto to the spark plug most ofthe noises are cut ofi ,even if the magneto is not itself shieldedalthough it is preferable that this be done.

The radiation from an ignition system consists That resulting from the'ignition current has a frequency of from 4 to megacycles and isadequately suppressed by the shielding means above described. However,the capacity of the spark plug is such that it sets up waves having alength of around one meter, that is, less than the usual length of theshielding apparatus, and radiation of such waves is not prevented by anyof-the shielding means heretofore used so far as is known to me.However, I have found that if a resistor iii of suitable value beinserted between the center electrode ll of the spark plug and theconductor IB of the ignition lead, that these waves of length less thanthe length of the shielding apparatus are likewise suppressed. If suchresistor be of too great value, it tends to damp out the long waves andthe ignition spark is too weak. My experiments have shown that if suchresistor have a value of about 100 ohms it renders the very short wavesaperiodic and effectively prevents radiation thereof, while it does notappreciably affect the strength of the ignition current.

The invention herein described and claimed may be used and/ormanufactured by or for the Government of the United States of Americafor governmental purposes without the payment of any royalties thereonor therefor.

I claim:

1. Radio shielding means for the ignition system of an internalcombustion engine, said system including a source of ignition current,comprising a plane ring disposed around the engine between the cylindersthereof and said source, said ring being mechanically and electricallycon-o nected to the engine, a foraminous electrically conducting membercooperating with said ring and the engine to enclose said source andgrounded on said ring, conducting leads extending from said sourcethrough said ring and other leads from said source extending throughsaid member, and a shielding element around each such lead, each saidelement being grounded at one end on said ring or on said member,respectively, and at the other end to the ground connection of therespective conductor.

2. Radio shielding means ror the ignition system of an internalcombustion engine having combustion chamber means and spark plug meanstherein, said system including a source of ignition current, comprisinga plane ring disposed around the engine between the said combustionchamber means and said source, a foraminous electrically conductingmember cooperating with said ring and engine to enclose said source andgrounded on said, ring, conducting leads extending from said sourcethrough said ring to said spark plug means, a resistive element betweeneach conducting lead and the spark plug means to which it suppliescurrent, and a shielding element around each such lead, each saidshielding element being grounded at one end on said ring and at theother end on the spark plug shell.

3. Radio shielding means for the ignition system of an aircraft internalcombustion engine, said system including a source of ignition current,comprising the combination with cowling around said engine of anelectrically conducting ioraminous screen extending across the spacewithin said cowling at one side of said source and grounded to saidcowling, a second like screen on the other side of said source extendingfrom said cowling to said engine and grounded to both, and shieldingelements around electrically conducting members extending through eithersaid screen, said shielding elements being each grounded at one end tothe respective screen and having the other end also grounded.

4. Radio shielding means for the ignition system of an aircraft internalcombustion engine having spark plugs, said system including a source ofignition current, comprising the combination with cowling around saidengine of an electrically conducting foraminous screen extending acrossthe space within said cowling at one side of said source and grounded tosaid cowling, a second like screen on the other side of said sourcevextending from said cowling to said engine and grounded to both,conducting leads from said source to said spark plugs, a resistivemember in series between each such lead and its respective spark plug,and a shielding element around each said lead grounded to a saidforaminous member and to the shell of the respective spark plug.

5. Radio shielding means for the ignition system of an aircraft internalcombustion engine having spark plugs, said system including a source ofignition current, comprising the combination with cowling around saidengine of an electrically conducting foraminous screen extend-v ingacross the space within said cowling at one side of said source andgrounded to said cowling, a second like screen on the other side of saidsource extending from said cowling to said engine and grounded to both,conducting leads from said source to said spark plugs, a resistivemember in series between each said lead and its respective spark plug,the value of said resistive member being suflicient to suppress waves ofthe order of those due to the capacitance of the spark plug butinsuflicient to reduce the current detrimentally, and a shieldingelement around each said lead grounded to a said foraminous member andto the shell of the respective spark plug.

6. Radio shielding means for the ignition system of an aircraft internalcombustion engine having spark plugs, said system including a source ofignition current, comprising the combination with cowling around saidengine of an electrically conducting foraminous screen extending acrossthe space within said cowling at one side of said source and grounded tosaid cowling, a second like screen on the-other side of said sourceextending from said cowling to said engine and grounded to both,conducting leads from said source to said spark plugs, a resistivemember in series between each said lead and its respective spark plug,the value of said resistive member being suflicient to suppress waves oflength not substantially greater than the distance between a saidforarninous member and the spark plug, and a shielding element aroundeach said lead grounded to a said 'foraminous member and the spark plugshell.

7. Radio shielding means for the ignition system of an internalcombustion engine, said system including a source of ignition current,comprising a foraminous electrically conducting member cooperating withsaid engine substantially to enclose said source and grounded throughsaid engine, conducting leads extending from said source through saidmember and a'shielding element around each such lead, each said elementbeing grounded at one end on said member and at the other end to theground connection of the respective conductor.

MELVILLE F. PETERS.

